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Technical Help Desk

VACUUM – For refrigeration applications 

Which Vacuum pump is best for my applications:

When it comes to selecting the correct vacuum pump for your application there are a number of issues that need to be considered:

  • Application – small or large systems
  • Frequency of use – daily or monthly
  • Speed required – long evacuation or fast
  • Ultimate vacuum required – deep vacuum is better for dehydration
  • Quality – do you do it once or have a few goes?
  • Your name – is it cheap or quality
  • Price – of course we have a budget but poor tools = poor trades

Small portable applications such as domestic refrigerators and freezers can easily be evacuated using a smaller vacuum pump, here the speed is not so critical but the portability is so vacuum pump in the 30 – 80 litre/min range will be adequate, of course it must be two stage or have the ability to achieve a deep vacuum.

Technology nowadays means a quality singles stage pump can easily out perform a low quality two stage, indeed many cheaper pumps are built as two stage so as to avoid the “blue printing” required for a quality vacuum pump.

For larger applications the 150 litre/min or 6CFM is ideal, it’s fast yet still portable enough for easy use. 

When it comes to larger commercial systems or chillers bigger is generally better so 300 – 500 litre/min is desirable, but be warned using a pump with a hose or inlet lines any smaller than the suction fitting opening on the pump will result is significant losses, pump manufacturers go to a lot of trouble to design the optimum inlet for there pumps so using a ¼ inch line of a 300 litre pump and over is a hindrance to it’s capability 3/8 is a minimum but ½ inch or ¾ will see significantly faster evacuations.

Also don’t think you can use one pump for several evacuations at once, its possible but the weakest or leakiest system will govern the vacuum of all in the group, multiple evacuation can actually take much be longer in practice. Most refrigerator production lines use an individual pump per refrigerator, yes hundreds of pumps per line – they know the rules. 

It is important that you also consider the type of protection required. The pump could be in a hazardous area, which could possibly cause an explosion if the motor is not of the correct protection class.

Of course if your not aware of this then you should seek professional advise!

As you can see there are a number of variations and performance elements that need to be taken into account when selecting a vacuum pump for your next job. If you are unsure about what is available or need assistance then please contact HVACDirect for expert advice. 

Experiencing Poor Vacuum?

Ultimate vacuum takes time, real time = quality. Fast short-term evacuation could come back to bite you and result in a failure down the line. The ultimate Vacuum is relative to pump capacity, quality, oil, and of course maintenance and lastly system size and integrity. If it appears the rotary pump is not achieving high vacuum, check as follows:

  • How good is your gauge?
  • Oil level correct when pumping.
  • All fitting hoses are tight and valves shut.
  • When was it last serviced

(like a car quality vacuum pumps need regular servicing)

If no improvement is achieved, check with a known good McLeod (reference) gauge or electronic gauge as follows: 

Remove pump from system.

Connect gauge to suction fitting positively sealed.

Run pump. A McLeod gauge should indicate a vacuum of between 50 and 1 micron. An electronic gauge will show approximately 250 to 20 micron after five minutes, depending on the type of pump.

The vacuum should be stead, if the vacuum is poor drain the pumps and use fresh manufacturers grade high vacuum pump oil ONLY. Ensure connections are secure. 

If the pump is good the problem is elsewhere.

Why your pump needs genuine vacuum pump oil: 

It is extremely important to operate your vacuum pump using the correct viscosity oil, as those that are either too thin or too thick will cause damage and operational issues.

Oil MUST be changed when contaminated.

Refrigeration compressor oil is not designed for vacuum pumps, don’t use it.

Oil contamination is usually indicated by poor vacuum reading, or a grey or milky appearance. Should liquids be accidentally allowed into the pump CHANGE OIL IMMEDIATELY. Your High Vacuum Pump is a precision unit and oil is less expensive than pump service and repairs. 

We take pride in every Vacuum Pump we supply and ensure you of our long-term interest in our product's reliability. To ensure your continued satisfaction, HVACDirect highly recommends OE oils.

If changing the oil hasn’t helped you pump should be serviced. 

I still can’t achieve a good vacuum.

How long have you, well it is system there may well be a larger number of joints, or possible leaky point, this can be checked using a tracer gas, ultrasonic leak detection or in the case of automotive systems a tracer fluid in the oil.

Why am I using a vacuum pump?

If you don’t know you really shouldn’t be doing this, but for the uninitiated any moisture that forms in a refrigeration circuit has the potential to freeze and create blockages, corrosion and thus inefficiency.

The vacuum doesn’t just remove the air it drys the system by reaching a pressure that allows the moisture to evaporate out of the circuit and oil thus creating a dry environment where by the HVAC system can achieve its maximum efficiency.

Dehydration is the correct term and it takes time as just one gram or 1 cc of moisture creates up to 1m3 of moisture vapour that the pump must remove and the pump needs to be hot so as to push through the moisture and not condense it in the pump it self, this evident when milky oil is in the pump, that milky appearance is moisture in the pump that will reduce vacuum and cause corrosion.

At cold temperatures this all takes longer, on hot days evaporation is fairly quick.

How long should I pump down for?

Good question, it is not a matter of time but really the vacuum you achieve and maintain, that’s why professionals use a quality vacuum gauges not just a guess.